This invention relates to a two-speed scroll compressor that is operable in a refrigerant system with an economizer function and other means of capacity modulation.
Refrigerant systems are utilized in many applications to condition an environment. In particular, air conditioners and heat pumps are employed to cool and/or heat a secondary fluid such as air entering an environment. The cooling or heating load of the environment may vary with ambient conditions, occupancy level, other changes in sensible and latent load demands, and as the temperature and/or humidity set points are adjusted by an occupant of the building.
Thus, refrigerant systems can be provided with sophisticated controls, and a number of optional components and features to adjust cooling and/or heating capacity. Known options include the ability to bypass refrigerant which has been at least partially compressed by a compressor back to a suction line. This function is also known as an unloader bypass function. This additional step in operation is taken to reduce system capacity.
Another option includes a so-called economizer cycle. In an economizer cycle, a main refrigerant flow heading to an evaporator is subcooled in an economizer heat exchanger. The main refrigerant flow is subcooled by a tapped refrigerant that is expanded to some intermediate pressure and temperature levels and then passed through the economizer heat exchanger. This tapped refrigerant is then returned to a compressor at an intermediate point in the compression cycle. Thus, the economizer cycle provides an additional step in operation to vary system capacity by switching between economized and other modes (or steps) of operation.
In the prior art, controls can be programmed to optionally actuate any one of these various control functions. However, the capacity provided by these functions is increased or decreased in relatively large discrete steps. It would be desirable to provide the ability to vary the capacity while the system is running at any of the above described modes of operation, in order to more closely match external load demands.
Motor drives are known for driving compressors at two speeds in a refrigerant system. By driving the compressor at a higher or lower speed, the amount of refrigerant that is compressed and circulated throughout the system changes, and thus the system capacity can be changed accordingly.
One increasingly popular type of compressors is a scroll compressor. In a scroll compressor, a pair of scroll members orbits relative to each other to compress an entrapped refrigerant. One design configuration of a scroll compressor utilizes both economizer and various unloader functions. Further, this scroll compressor may employ a single intermediate port to provide both functions alternatively or simultaneously. This scroll compressor is disclosed in U.S. Pat. No. 5,996,364.
However, scroll compressors have not been utilized in combination with a two-speed drive for its motor and an economizer cycle to obtain additional flexibility in system operation and control.